Disassembly Mechanisms and Energetics of Polymetallic Rings and Rotaxanes

Understanding the fundamental reactivity of polymetallic complexes is challenging due to the complexity of their structures with many possible bond breaking and forming processes. Here, we apply ion mobility mass spectrometry coupled with density functional theory to investigate the disassembly mechanisms and energetics of a family of heterometallic rings and rotaxanes with the general formula [NH2RR’][Cr7MF8(O2CtBu)16] with M = MnII, FeII, CoII, NiII, CuII, ZnII, CdII. Our results show that their stability can be tuned both by altering the d-metal composition in the macrocycle and by the end groups of the secondary ammonium cation [NH2RR’]+. Ion mobility probes the conformational landscape of the disassembly process from intact complex to structurally distinct isobaric fragments, providing unique insights to how a given divalent metal tunes the structural dynamics.


■ INTRODUCTION
Ion mobility mass spectrometry (IM-MS) allows both the mass and structure of isolated ions to be measured in the same experiment. 1−4 Ion mobility measurements for any given analyte can be converted to the structural parameter collision cross sections (CCS), which can be compared to those predicted from theoretical candidate geometries. IM-MS has been widely applied to examine the dynamics of the disassembly of protein complexes 5−8 but far less often to determine the relationship between conformation and stability of synthetic macromolecular complexes. A number of studies have demonstrated the use of IM-MS for the characterization of polymetallic compounds, 9−15 but only a handful have used it to explore disassembly processes. For example, Wesdemiotis and co-workers showed the collisional activation of a terpyridine-based hexameric Cd-complex and subsequently used ion mobility to separate the macrocyclic precursor ion from linear isomers. 16 In another study, Mallis et al. investigated pyridine-based Pt-rhomboids and demonstrated, among other things, different gas phase stabilities of isobaric complexes with activated IM-MS. 17 More recently, Baksi et al. used IM-MS to visualize the energetically driven reaction between coin metal thiolate clusters, in which silver atoms were incrementally exchanged for gold centers. 18 Although these are interesting examples, a systematic application of IM-MS to investigate the reactivity or disassembly of polymetallic complexes as a function of structure and metals present has not yet been reported.
We hypothesized that IM-MS would be an ideal method to investigate these systems and that it could be used to rationalize the stability of isostructural complexes as a function of the metal present along with conformation-specific information. An attractive chemical problem to answer with this approach is the conformational rigidity of rotaxanes with respect to their threads (herein used as a synonym for "axles"). To address these challenges, we use IM-MS supported by density functional theory (DFT) to characterize the heterometallic rings [Cr 7 MF 8 (O 2 C t Bu) 16 ] − ("[Ring M ] − ", M = Mn II , Fe II , Co II , Ni II , Cu II , Zn II , Cd II ) alone as well as in hybrid organic−inorganic [2]-rotaxane families of the formula [NH 2 RR'][Ring M ] ("Ph M " and "Am M "), where R and R' are terminated by bulky phenyl or tert-butyl groups such that the secondary ammonium cation threads through [Ring M ] − (Ph M : thread "TPh + " ("Phenyl") = [NH 2 (CH 2 C 6 H 5 )-(CH 2 CH 2 C 6 H 5 )] + ; Am M : thread "TAm + " ("Amide") = [NH 2 (C 6 H 12 NHC(O) t Bu) 2 ] + ). The studied compounds and their building blocks are illustrated in Table 1.
In our analysis, we consider if the Irving−Williams series and other arguments, often developed for monometallic complexes and rationalized by crystal field theory, are transferable to polymetallic complexes. We show that IM-MS can qualitatively and quantitatively investigate the disassembly, conformational dynamics, and stabilities of these compounds. The specific systems studied have been proposed as qubits for quantum information processing, 19 and the ability to link the rings into multiple qubit arrays 20 is a key advantage that this approach has over more conventional approaches. Understanding the stability of the compounds is important in order to make increasingly complex molecules for specific quantum applications, e.g., synthesis of a five-spin supramolecule that could be used to simulate decoherence in Bell states. 21 As supramolecular chemistry using polymetallic units as building blocks develops, 22 16 The heterometallic rings [Ring M ] − studied consist of seven chromium(III) ions and one divalent metal center, arranged in a regular octagon with each edge bridged by one fluoride inside the ring and two pivalate ligands (O 2 C t Bu = Piv) outside the ring (Figure 1a, inset for M = Mn II ). 26 On each edge, there is one axial and one equatorial pivalate, with respect to the Cr 7 M plane, with the axial position alternating "up" and "down" around the ring. Following optimization of the ionization source and solvent conditions, mass spectra of [NH 2 RR']-[Ring M ] (R = R' = CH 3 for M = Mn II , Co II , Ni II , Cu II , Zn II , Cd II and R = R' = C 2 H 5 for M = Fe II ) were recorded in positive and negative modes. For all species, intact rings were observed as anions ( Figure S1a  Disassembly and Stability Trend of [Ring M ] − . To understand how altering the d-metal composition affects the ring energetics, we isolated each ring and ramped the energy at which it is activated by collisions while recording the arrival time distribution (ATD) of the precursor and product ions. We extracted the CCS as a function of the collision energy for all ions. In the tandem mass spectra (MS 2 ), common product ions were observed, indicating similar fragmentation pathways. For example, the precursor ion [Ring Mn ] − at m/z = 2188 follows dissociation channels that all involve the loss of a metal center along with ligands (Figure 1a), suggesting substantial perturbation of the ring geometry. We identified the products and reaction pathways including the loss of the manganese and two pivalate ligands (reaction to [Cr 7 F 8 Piv 14 ] − = 1), the loss of one chromium center, two pivalates and one fluoride (reaction to [Cr 6 MnF 7 Piv 14 ] − = 2), or one chromium and three pivalate ligands (reaction to [Cr 6 MnF 8 Piv 13 ] − = 3, Figure 1a). Ion mobility allows us to consider the conformations of the precursor and product ions. While [Ring Mn ] − presents a discrete unimodal conformer centered at CCS N2 = 438 Å 2 at this collision energy, remarkably for all fragmentation channels, the product ions are structurally diverse, with narrow, unimodal conformers at lower CCS N2 (compact, "C") as well as wide, multimodal distributions with higher CCS N2 (extended, "E", Figure 1b). The nature of these disassembled products is investigated further below.
For all [Ring M ] − (M = Mn II , Fe II , Co II , Ni II , Cu II , Zn II , Cd II ), the fragmentation behavior is similar and results in 1 as the main product. This preference for 1 over the structures similar to 2 and 3 (different M) is more pronounced for Ni II , Zn II , Cd II , and particularly Cu II (Supplementary Data Set). The energy needed to break the [Ring M ] − structure, predominantly yielding 1, also varies ( Figure 1c) and was quantified with E 50 values (Table S1, Figure 1d) obtained from the corresponding survival yield plots (Figure 1c) Figure S2 for M = Mn II ), from which we obtained CCS N2 values using the trajectory method of IMoS. 27 These were found to be ∼8% larger than experiment (Table S2). To investigate this slight discrepancy, two hypothetical ring conformers ( Figures S3 and S4) Figures S8 and S9).
As discussed above, changes in arrival time distribution of [Ring Mn ] − were recorded as a function of incremental increases in collision energy, showing the onset of ring dissociation and the corresponding appearance of fragment ions ( Figure S10). Although there is little evidence of any substantial change in the conformation of the ring prior to dissociation, at low energies, [Ring Mn ] − contracts slightly before expanding again. The product ions present distinct conformational families C and E (Figure 1b). The relative population of these distributions differ significantly between the fragments but also with respect to the divalent metal M as observed from measurements on other [Ring M ] − precursors (Supplementary Data Set). Surprisingly, the relative populations of C and E in the homometallic Cr 7 -fragment 1 allow us to distinguish which divalent metal M was present in the precursor [Ring M ] − . Significant amounts of 1C are observed for Cu II , Zn II , and Cd II ( Figure S11 for M = Cu II ), whereas almost no 1C is seen for Mn II , Fe II , Co II , and Ni II (Figures S12 and S13 for M = Mn II , Ni II ). For the less dominant product ions 2 and 3, the observed differences between M are more subtle.
To rationalize this behavior, additional experiments and calculations were carried out for fragment 3 with M = Mn II . Each distribution was selected, reinjected in the drift ring, and again, ion mobility separated in one to three passes (IMS 2 ).  (Table S1). Error bars are shown and in most cases are smaller than the symbol size.
For 3C, no further change is seen to the ATD, even after three passes, suggesting that this conformer is highly stable and does not interconvert ( Figure S14). For the extended distribution 3E, multiple passes broaden the ATD, but no further  Figure S29). Error bars are omitted for clarity but in all cases are smaller than the symbol size (Table S1). The electron configuration of Fe depends on the oxidation state (Fe II : 3d 6 , Fe III : 3d 5 ). resolution is achieved, indicating that this feature contains interconverting species that are conformationally dynamic on the experimental timescale (∼250 ms, Figure S15). We also examined how collision energy influences the population of these features in the activated IM-MS spectra of [Ring Mn ] − . For all fragments 1−3, the C distributions form and subsequently dissociate at slightly lower E lab than the extended distributions E ( Figure S16). DFT calculations were performed to discern the structures of the 3 conformers (Table S4), including a seven-membered Cr 6 Mn-ring as a candidate for 3C ( Figure S17) and different opened helical forms as candidates for 3E (Figures S18−S22). A comparison between their predicted CCS N2 values with those found experimentally is instructive in understanding the disassembly processes for [Ring M ] − (see below).  (Table S1 and Figure 2c), as well as for [Ph Fe(III) ] + and [Am Fe(III) ] + , which showed the same disassembly pathway ( Figure S30). The results demonstrate that three factors influence the stability of the rotaxane ions [Ph M + A] + and [Am M + A] + : first, the metal M in the heterometallic ring and its oxidation state, second, the thread and its end group (TPh + vs TAm + ), and finally, the charge carrying species A + (A + = H + , Na + ), where we observed a significant difference between protonated species and sodiated forms. The impact of these and other charge carriers on the disassembly, stability, and conformations of these complexes is the subject of another report. 28 Ion Mobility   As discussed before, the fragmentation channels are similar for both ions and involve the loss of the thread and one anionic ligand (F − : 4, 6 and Piv − : 5, 7). The ATD of the precursor ions [Ph Cd + Na] + and [Am Ni + Na] + as well as their direct fragments 4−7 were converted to CCS N2 (Figure 3b), showing that [Am Ni + Na] + is 9% larger than [Ph Cd + Na] + due to the  (Figure 4 center). The increased stability from Mn II (3d 5 ) to Ni II (3d 8 ) is attributable to the increasing effective nuclear charge and occupation of the stabilizing t 2g -orbitals in the octahedral crystal field. For Cu II , Zn II , and Cd II , the reverse trend would be expected due to occupation of the destabilizing e g -orbitals and for Cd II because of a larger ionic radius (Zn II vs Cd II , Figure 1d and Table S1). Small deviations from this trend are shown by Mn II , which we would predict to be less stable than Fe II (3d 5 vs 3d 6 ), and also by Cu II , which should be more stable than Zn II (3d 9 vs 3d 10 ). We suggest that the repulsive forces between the pivalate ligands are less in [Ring Mn ] − than for the other rings because of the larger ionic radius for Mn II , compensating for the smaller Mn II −O bond energy. 30 The lability of [Ring Cu ] − is a result of Jahn−Teller distortions causing the elongation of one of the F−Cu II −O axes, 31 which is well-known from other Cu II complexes and its impact on periodic stability trends previously reported. 32,33 Jahn−Teller effects could also make [Ring Cu ] − more flexible, as observed before for related containing five-coordinate Cu II sites. 34 Notably, our data agree well with the M II trend for water-exchange reaction rate constants of the hexaaqua ions [M II (H 2 O) 6 ] 2+ (Table S5, Figure S32), although a different stability trend from ESI-MS experiments has recently been reported for supramolecular terpyridine-based fractal complexes (Ni II > Co II > Zn II > Fe II > Cu II > Cd II > Mn II ), indicating that the electronic environment of M II may be altered in the case of some ligands. 35 Figure S33). A difference between the metal trends of the sodium adducts and the ring anions are the species with M = Zn II and Cd II , where we observe a higher stability for M = Cd II in both. Cd II is the only 4d metal in this study and its bigger size and lower charge density might lead to a more favorable chelation of the sodium cation and/or stronger H−F hydrogen bonds in the thread resulting from weaker Cd II −F bonds.

Sodiated Rotaxane Ions [Ph M + Na] + and [Am
The thread and its functionality have a significant impact on the E 50 values of the sodiated ions [Ph M + Na] + and [Am M + Na] + (Figures 2b and 4 bottom, Table S1). The ions [Am M + Na] + are all more stable than [Ph M + Na] + , which can be attributed to both steric and electronic effects. The tert-butyl groups in TAm + are larger than the phenyl end groups in TPh +36 , making it harder for the thread to dissociate from the ring. Further, the amide end groups will form stronger charge− charge interactions with the macrocycle than the phenyl groups, making [Am M + Na] + more stable. We also examined [Ph Fe(III) ] + and [Am Fe(III) ] + ( Figure S30), which allows us to consider the effect of oxidation state when compared to the divalent metals M II . These exhibit strongly enhanced stabilities resulting from stronger charge−charge interactions of Fe III and the absence of an additional cation, which presumably weakens the M−O and M−F bonds (Figure 2c).

Protonated Rotaxane Ions [Ph M + H] + and [Am M + H] + .
The fragmentation of the protonated rotaxane ions takes place at significantly lower E 50 values (Figure 2c) than the sodiated forms and also leads to a different fragmentation pathway, which always involves the loss of one pivalic acid ( Figure S24). Protonation followed by pivalic acid dissociation is more likely on a carboxylate oxygen bound to M II than one adjacent to Cr III due to higher charge density on the O-donor, which is why the E 50 values of [Ph M + H] + and [Am M + H] + depend also on the divalent metal M II (Figure 4 top). The E 50 trend agrees well with the Irving−Williams series across the measured 3d-metal rings, 41 with the exception of Cd II which is not part of the Irving−Williams series as it is a 4d metal and shows a smaller E 50 value than Zn II (both d 10 ).This is presumably because of its larger size that destabilizes the M II − O bond (Table S1) Figure S10a). The ATD for each fragment are diagnostic and support disassembly into two conformational forms: a compact, rigid species C and an extended, flexible species E (Figure 1b). The relative intensities of the bimodal ATD found for product ions 1−3 alter with the number of pivalate ligands. For 1 and 2, the metal centers proximal to the cleavage point now possess two pivalate groups and repulsive interactions between these bulky ligands could lead to the preference of extended conformations (1E and 2E: CCS N2 ≈ 412−463 Å 2 , Figure 1b). Conversely, 3 has only one remaining pivalate ligand at the cleavage point, which could preferentially rearrange to be closer to the metal center, resulting in a more contracted conformation (3C: CCS N2 = 394 Å 2 ). IMS 2 experiments on the extended species 3E did not provide any better separation after multiple passes in the cyclic drift ring, indicating that 3E contains a dynamic equilibrium of interconverting conformers ( Figure S15).
The collected data suggest that two disassembly mechanisms occur for [Ring M ] − (Figure 4 center), depending on both M (Figures S11−S13) and the collision energy ( Figure S16). The Journal of the American Chemical Society pubs.acs.org/JACS Article metals with smaller E 50 values, namely, Cu II , Zn II , and Cd II (Figure 1d), have a stronger tendency to form 1 over 2 and 3 and also to yield 1C over 1E. This argues that this low energy mechanism leads only to minor ring disruption, favoring retention of compact conformers C. For the divalent metals with higher E 50 values, more 1E is seen, indicating a greater perturbation of the structure. The fact that Cu II , Zn II , and Cd II decompose more to C than the other metals can be explained with their size (Cd II ) and their tendency to form complexes with lower coordination numbers, facilitating the departure of the metal center without major ring disruption. Surprisingly, the divalent metal M in the precursor [Ring M ] − , influences the conformations seen for the main fragment 1, despite 1 only containing chromium (Figures S11−S13). This strongly suggests that the stability of the leaving group {MPiv 2 }, and the ease with which it can depart, is a driving factor for the preference of C or E, agreeing with the relative preference of Cu II , Zn II , and Cd II for tetrahedral coordination geometries. We hypothesize that the contracted conformers C are sevenmembered rings (Figure 4 center), which have been reported once previously, for a Cr 6 Ce ring where the large ionic radius of the heterometal was crucial. 38 Such species, assuming a similar connectivity as for [Ring M ] − , can most easily form when exactly three ligands are present per metal center as in 2 and 3, which would explain the preference for 1E over 1C. The broader peaks at higher CCS N2 could correspond to extended horseshoe structures with seven metal centers, which are more common than the closed seven-membered rings in solution. 39 Informed by the structures obtained from DFT and their predicted CCS N2 , we can rationalize the disassembly process of [Ring Mn ] − . On the basis of systematic differences for each [Ring M ] − , we apply a scaling factor of 0.92 to all predicted CCS N2 values for hypothetical fragment structures of 3 (Table  S4). These scaled CCS N2(s) values of a Cr 6 Mn-ring ( Figure  S17) and a slightly opened helix ( Figure S20) agree well with the experimental CCS N2 of 3C, suggesting that only minor ring perturbation takes place. By contrast, the CCS N2(s) of the more open helical conformers ( Figures S21 and S22) are in the experimental CCS N2 range of 3E, agreeing with our predictions that these are highly disrupted opened ring structures.
Sodiated Rotaxane Ions [Ph M + Na] + and [Am M + Na] + . The disassembly of the sodiated rotaxanes involves the loss of the thread (TPh + or TAm + ), for which two mechanisms can be considered. The first proceeds by an opening of the ring structure followed by thread release, and the second proceeds by a slipping mechanism through the cavity of the ring. The latter is relatively small for [Ring M ] − compared to common organic macrocycles, largely because of the bulky pivalate ligands, and [Ring M ] − therefore appears to hold the thread even with small stopper groups such as in TPh + and TAm + (Figure 2b). Space-filling models of the crystal structures Ph Cd and Am Ni 29 suggest that the cavity of the ring (diameter ≈ 3.5 Å) and the R and R' groups (width ≈ 5.8−5.9 Å) will not permit a slipping mechanism ( Figures S35 and S36, Table S6). We previously studied the kinetic stability of Am Co where we added a similar, isotopically labeled rotaxane at 60°C. No ring or thread exchange occurred between the molecules after stirring the solution for one week. 29 These data did not point to a slipping mechanism for disassembly in solution, but ambiguity in the analysis from new bulk phase measurements warranted further investigation.
The observed gas phase stability trends for [Ph M + Na] + and [Am M + Na] + (Figure 2c) are similar to the one obtained for the [Ring M ] − series (Figure 1d) as the stability of M−O and M−F bonds likely determines the E 50 value here as well. This can be due to either bond breaking or lengthening and does not help to determine the dethreading mechanism. The evidence from ion mobility measurements is more useful, and following thread loss, the rotaxane ring fragments (4−7) present have narrow ATD, indicative of compact structures with no evidence of extended conformers as seen for [Ring Mn ] − (Figure 1b). In the ion mobility heat maps of [Ph Cd + Na] + and [Am Ni + Na] + (Figure 3a), the observed precursor ATD narrows between E lab = 60−90 eV, which suggests minimal disruption of the ring structure prior to the loss of thread.
Our hypothesis, therefore, that the ring has widened prior to thread release is further strengthened by comparison of the CCS N2 distributions of fragments 4 and 6 ( Figure 3b Considering that the thread end groups in both Am M and Ph M are significantly larger than the ring diameter, as shown by space-filling models from the crystal structures (Figures S35  and S36, Table S6), this result is noteworthy and warrants further investigation.

■ CONCLUSIONS
We have shown that energy-resolved MS 2 and IM-MS coupled with DFT combine effectively to characterize polymetallic complexes in the gas-phase, yielding information on the compounds' disassembly, energetics, and conformational dynamics. Our study demonstrates that these methods, more commonly applied to the disassembly of protein complexes, 6,40−43 can be usefully applied for supramolecular and inorganic chemistry. The results show that the stability of the studied ring and rotaxane ions is tuned by altering the d-metal composition in the heterometallic ring, the end groups in the thread, and the charge carrying ion, providing a framework to follow in for the future design of self-assembled polymetallic complexes.
IM-MS was applied to investigate the dissociation mechanism of the rotaxane ions in the gas phase, suggesting that the thread slips through the cavity of the ring after bond lengthening near M. Examination of the [Ring M ] − disassembly with IM-MS disclosed two mechanistic routes, leading to compact seven-membered rings as well as conformationally dynamic open horseshoes. Perhaps most curiously, we find that the structure of the homometallic fragment 1 = [Cr 7 F 8 Piv 14 ] − is differentiated into compact or extended product ions depending on the divalent metal in the precursor ion, even though M is no longer present.
For all studied species, the trends in stability and ensuing disassembly mechanisms can be rationalized using concepts from crystal field theory, demonstrating that classic observations such as Jahn−Teller effects and the Irving-Williams series are applicable to large polymetallic compounds. Extending this to include ligand field theory would suggest other factors such as interelectronic repulsion (the nephelauxetic effect), spin− orbit coupling and variation in bond lengths could be evaluated. 44 In the future, it may be possible to compare the simple crystal field theory explanation here with a more sophisticated ligand field theory approach. For now, we conclude that the use of IM-MS coupled with ab initio calculations to examine (metallo-)supramolecular complexes has considerable promise. 13 subsequently transferred (transfer energy: 4−15 V) to a time-of-flight mass analyzer. Details of this method known as traveling-wave ion mobility spectrometry (TWIMS) can be found elsewhere. 3,48−50 Data Processing. Mass spectra were recorded for different kinetic energies, and the survival yield (SY) of each precursor ion was calculated from its absolute intensity (I P ) and the sum of the fragment ion intensities (I F ) according to eq 1: Additionally, laboratory kinetic energies E lab were converted to center-of-mass energies E com using eq 2. This relationship assumes a single collision of the stationary target gas with the mass m g , for this work nitrogen, with the accelerated precursor ion of the mass m p . Under these conditions, the maximum amount of kinetic energy accessible for the conversion to internal energy is given by E com . 51 The center-of-mass energy where SY = 0.5 (or 50%) can be defined as E 50 , which is known as a relative measure of precursor ion stability in the gas phase. Experimental parameters (trapping gas pressure, temperature, and pre-CID voltages) are maintained constant in order to obtain comparable and meaningful E 50 values across different precursor ions; however comparisons across different instruments are not trivial. 52 E 50 values are derived from plots of SY vs E com by using a fit with a sigmoidal Hill function (Hill1 function in OriginPro 2020b). For some of the studied protonated forms, contaminating species overlapped and showed significantly different stabilities. In these cases, the share of the contamination was subtracted in the survival yield plots before fitting.
Activated ion mobility mass spectrometry data obtained from a Select Series Cyclic IMS instrument (Waters) were not converted to E com . Experimentally obtained arrival time distributions were converted to nitrogen collisional cross sections ( TW CCS N2 , TW = "Traveling Waves") via published calibration procedures. 53 The Agilent tune mix was used for all TW CCS N2 calibrations. 54 Density Functional Theory and Collision Cross Section Calculations. All DFT calculations were carried out with Gaussian 16 55 utilizing the B3LYP exchange-correlation functional with the Grimme D3 empirical dispersion correction. 56 An effective core potential and its associated split valence basis set were used for transition metals (LANL2DZ), 57 and a 6-31G(d) basis set on other atoms. All structures were optimized to the default convergence criteria (RMS force <3·10 −4 E h /a 0 ), and the conformers were confirmed to be the minima by vibrational analysis with corresponding formate models (O 2 CH − instead of O 2 C t Bu). Metal electronic states were high spin, as found experimentally, with low deviations from <S 2 > although they were ferromagnetically coupled. Atomic charges were obtained for the optimized structures at the same DFT level using the Merz−Kollman method with UFF-based radii as implemented in Gaussian 16.
Theoretical collision cross section values ( TH CCS N2 , TH = "Theoretical") were obtained from the software IMoS by using the trajectory method in nitrogen gas including quadrupole potential (number of orientations: 3, gas molecules per orientation: 300,000, temperature: 298 K, pressure: 101,325 Pa = 1 atm). 27 Crystallographic Data. Single crystal XRD data was collected on an Agilent SuperNova CCD diffractometer with Mo Kα radiation (λ = 0.71073 Å) and a Rigaku FR-X with Cu Kα radiation (λ = 1.5418 Å) equipped with a Hypix6000HE detector. Data was measured using the CrysAlisPro suite of programs 58 and was solved using the SHELXL and Olex 2 suite of programs. 59,60 ■ ASSOCIATED CONTENT

Data Availability Statement
The supplementary data set is available on Figshare 10.6084/ m9.figshare.20324448 and contains the raw ion mobility mass spectrometry and mass spectrometry data files as well as the outputs from DFT calculations.
Mass spectrometry, tandem mass spectrometry, and ion mobility mass spectrometry data of [Ring M ] − , [Ph M + A] + , and [Am M + A] + as well as related data; density functional theory studies and predicted collision cross sections of [Ring M ] − , its conformers and of fragment 3; crystal data and studies of Ph M and Am M ; synthetic procedure for Ph M (PDF)